The present disclosure relates to air filters for HVAC systems. More particularly, it relates to systems and methods for predicting the need to change or replace an air filter in an HVAC system, such as in a residential, demand-operation HVAC system.
Heating, ventilation, and air conditioning (HVAC) systems are commonly used to control temperature and air quality in the interior space of various dwellings, such as homes, buildings and other structures. With many HVAC installations, a disposable air filter is conventionally employed. Such filters often include a frame and a fibrous filter material, and may include a reinforcing structure to help support the filter material. After a period of use, these filters become dirty or clogged and must be replaced. Proper filter maintenance helps keep the HVAC system operating at maximum efficiency, reduces operating costs, and better ensures desired indoor air quality; further, continuing to run an HVAC system with an excessively clogged filter can negatively affect the expected useful life of various HVAC system components.
Many non-expert HVAC system users (e.g., homeowners) cannot readily ascertain whether the air filter needs to be replaced by simple inspection and/or do not regularly inspect the air filter. To help such users avoid the problems described above, filter manufacturers recommend replacement on a regular, fixed-interval basis, and in particular a fixed calendar period of time. The fixed interval replacement approach is easy to remember and follow, and the recommended time period is typically based on extensive studies of air filter performance under normal conditions. With this approach, the filter is replaced after a certain recommended fixed calendar period of time, such as three months, has passed. This fixed period of time, however, may not be appropriate for all situations, and in particular with demand-operation HVAC systems (typically employed with residential homes and light commercial dwellings) in which the HVAC system's fan only runs (and thus airflow is presented to the air filter) when the controller is calling for heating or cooling. Under these circumstances, the actual runtime of the HVAC system over the course of the fixed calendar period of time will often vary with the season of the year. As a result, the fixed period may be too short, in which case the air filter is discarded prematurely, or the fixed period may be too long, in which case the air filter is used beyond the time when it should have been changed. Numerous other environmental factors (e.g., airborne particulate levels, user preferences, etc.) may further contribute to deviations between actual filter loading vs. expected at the end of the recommended fixed period of time.
Regardless of whether the recommended fixed period is too short or too long as compared to the actual runtime of the HVAC system, some HVAC system users (e.g., a homeowner) may view the recommended three month (or other) fixed interval filter change as being overly cautious and decide not to follow the recommendation. Others may simply forget to make record of the recommended replacement date. Absent an overt indication that the HVAC system is not operating as expected due to a possibly clogged filter, many users will purposefully or unintentionally not change the air filter until after the air filter is beyond its useful life.
In light of the above, various devices have been devised that indicate a replacement status or need for filter change based on an actual condition of the filter. For example, some filter manufacturers provide color-change indicia or dirty filter pictures/illustrations on the air filter frame and/or packaging to indicate the stage at which the air filter needs to be changed. While these filter change strategies attempt to more closely tie the filter change to actual filter condition, they are not very able to accommodate different kinds of indoor air contaminants that may greatly affect the visual appearance of the air filter. Further, these techniques require the user to remember to visually inspect the air filter in order to determine status.
In other HVAC installations, a digital thermostat is provided, programmed to generate filter change reminders based on actual run hours. The thermostat directly controls the HVAC system and can readily track the number of hours the air filter has processed indoor air; the thermostat's display can indicate to the user when the air filter needs to be changed. Several models of room air cleaners also employ a similar change strategy, using run hours to indicate the need for change. This filter change approach can be a viable option for those users already owning a programmed or programmable digital thermostat. However, the purchase and retro-fit installation to a conventional HVAC system (that does not otherwise include an appropriate digital thermostat) can be expensive and time-consuming.
Another known approach for generating filter status information is premised upon a sensed or monitored pressure drop across the air filter. The pressure drop will increase as the air filter becomes clogged with particles, such that an elevated pressure drop indicates a need to replace the air filter. One such system is provided as after-market product (for installation to an existing HVAC system), and includes a mechanical filter pressure indicator that must be installed between the blower and the filter where a slight vacuum exists and indicates the filter pressure drop to the user. While viable, the user is required to form one or more holes into the HVAC ductwork (e.g., one or more drilled holes) and to preform initial calibration. Due to the numerous variants of HVAC equipment and installation methods, different filters, different airflow in heating and cooling modes, the need for sensor installation, and frequent lack of readily accessible electrical power near the HVAC system, these and other aftermarket indicators are less than optimal.
In light of the above, a need exists for a simple, low-cost system and method of more accurately predicting and communicating the need for filter change in an HVAC system, such as demand-type HVAC system applications.